Light year
From the Simple English Wikipedia, the free encyclopedia that anyone can change
A light year (or light-year or lightyear) is not a length of time, but the distance that light will travel in one Earth year (365 days), going at the speed of light. One light year is about 6 trillion miles, or 10 trillion kilometers. Because the universe is so big, some things are hundreds, thousands or millions of light years away. Because light that leaves a star 100 light years away will take 100 years to get to us, this means that when we see the star's light, we are actually seeing that star as it was 100 years ago.
